Slow Regex HTML_BLOCK_ELEMENT_R because of issue with self closing tags

[devbrains-com]

We found out, the following regex is very slow and takes up to 50ms with a single self closing tag on the page.

const HTML_BLOCK_ELEMENT_R = /^ *(?!<[a-z][^ >/]* ?\/>)<([a-z][^ >/]*) ?([^>]*)\/{0}>\n?(\s*(?:<\1[^>]*?>[\s\S]*?<\/\1>|(?!<\1)[\s\S])*?)<\/\1>\n*/i

The reason for that seems to be a non working check for self closing tags \/{0}.

The final regex would be:

const HTML_BLOCK_ELEMENT_R = /^ *(?!<[a-z][^ >/]* ?\/>)<([a-z][^ >/]*) ?((?:[^>]*[^/])?)>\n?(\s*(?:<\1[^>]*?>[\s\S]*?<\/\1>|(?!<\1)[\s\S])*?)<\/\1>\n*/i

Thank you very much

[quantizor]

Could you check again with the latest code? There was a sorting issue in the rules that might have contributed to this problem.

I did perf test this particular change and was getting inconclusive results https://jsperf.app/joribi/1/preview

[devbrains-com]

Thank you very much for looking into it. It seems like the sorting fixes our main concern.

The regex's performance improvement was only visible in large examples with a lot of text after the self-closing element. I tested again, and I couldn't see any performance difference now.

[Goues]

Hey, here is a repro https://regex101.com/r/ac4mJP/1

Apparently, self closing tags cause a runaway regex and it just times out eventually if there is enough content. The fix proposed in here does fix this issue. Would you care to reopen the issue?

[quantizor]

@Goues if you run the adjusted regex against the unit tests it bails too early, but it is a lot faster. Working on finding a happy medium.

Worth noting that the OP regex is not current (there's no \/{0} sequence anymore). The current block HTML regex is:

/^ *(?!<[a-z][^ >/]* ?\/>)<([a-z][^ >/]*) ?([^>]*)>\n?(\s*(?:<\1[^>]*?>[\s\S]*?<\/\1>|(?!<\1\b)[\s\S])*?)<\/\1>(?!<\/\1>)\n*/i

[quantizor]

Ok I found a variation that works better

/^ *(?!<[a-z][^ >/]* ?\/>)<([a-z][^ >/]*) ?((?:[^>]*[^/])?)>\n?(\s*(?:<\1[^>]*?>[\s\S]*?<\/\1>|(?!<\1\b)[\s\S])*?)<\/\1>(?!<\/\1>)\n*/i

Thanks all, will get this into v7